Mäki published his first novel Enkelipölyä in 1985. His most well-known character is private detective Jussi Vares who was first introduced in the novel Moukanpeli released in 1986. A total of 25 novels about Jussi Vares have been published to date (in addition to his other non-Vares books). All novels take place in the portuary city of Turku , and in its grim granite jail, Kakola prison (maximum security prison, abandoned in 2007, see http://abandonedplaces.livejournal.com/2589107.html). Nine of the Vares novels have been made into feature films. The first two (2004-2007) feature Juha Veijonen as Jussi Vares. The next seven (2011-2015) feature Antti Reini; the first six of these (2011-2012) have been released on DVD in Region 1. Some films have been released in movie theaters in Finland and some straight-to-DVD.

Mäki is one of the most influential modern Finnish authors. His most recent novel Cowboy was released in 2014 and is the final book in a trilogy (the other two are Sheriffi and Intiaani).